System for maintaining accumulator pressures within close limits



Aug. 9, 1955 R. TYLER SYSTEM FOR MAINTAINING ACCUMULATOR PRESSURES WITHIN CLOSE LIMITS Filed March 28, 1952 To Circuit INVENTOR RANSOM TYLER ATTORNEY United States Patent SYSTEM FOR MAINTAINING ACCUMULATOR PRESSURES WITHIN CLOSE LIMITS Ransom Tyler, Greenfield, Wis., assignor to The Oilgear Company, Milwaukee, Wis., a corporation of Wiscousin Application March 28, 1952, Serial No. 279,047

Claims. (Cl. 103-41) This invention relates to the control of pressures in fluid systems and it is particularly adapted for maintaining the pressures in hydraulic accumulators within close limits.

A hydraulic accumulator is ordinarily charged by liquid supplied thereto from a pump and the flow of liquid from the pump to the accumulator is alternately established and discontinued in response to operation of a pressure responsive electric switch. A commercial type pressure switch when adjusted either to open or to close at a given pressure will either open or close at substantially that pressure but there is a wide differential, such as ten per cent, between the pressure at which it will open and the pressure at which it will close so that there is a wide differential, such as ten per cent, in the pressure maintained in the accumulator.

An object of the present invention is to maintain the pressures in fluid systems and particularly in systems which include accumulators within close limit such as one per cent or" the desired pressure.

Advantages and more specific objects of the invention will appear from the following description of the embodiment of the invention shown schematically in the accompanying drawing in which the views are as follows:

Fig. 1 is a diagram of the hydraulic and electric circuits of a system for maintaining the pressure in an accumulator within close limits.

Fig. 2 is a diagram of a portion of the hydraulic circuit shown in Fig. 1 but showing a valve in a different position.

The invention has been shown as being employed to maintain within close limits the pressure in an accumulator 1 which is connected by a channel 2 to a hydraulic circuit not shown. Liquid for charging accumulator 1 is supplied thereto by a pump 3 which draws liquid from a reservoir 4 and discharges it into a channel 5 which is I connected to accumulator 1 and has a check valve 6 and a resistance 7 connected therein.

Delivery of liquid to accumulator 1 is controlled by a valve having a valve member 8 fitted in a body 9 and urged toward the left in respect to the drawing by a spring 10. The stem of valve member 8 has been shown connected to the armature of a solenoid 11 which when energized will move valve member 8 toward the right into the position shown in Fig. 2 but, if pump 3 is of such size that a large valve is required, valve member 8 is shifted hydraulically under the control of a pilot valve according to common practice and the armature of solenoid 11 is connected to the stem of the pilot valve. Solenoid 11 is controlled by a magnetic switch or contactor C1 operation of which is controlled by two pressure switches PSH and PSL.

Valve member 8 controls communication between one end of a channel 15, which has its other end connected to pump 3 as by being connected to channel 5 at a point between pump 3 and check valve 6, and one end of a channel 16 the other end of which extends into reservoir 4. Valve member 8 also controls communication be- 2,714,854 Patented Aug. 9, 1955 tween one end of a channel 17, which has its other end connected to accumulator 1 as by being connected to channel 5 at a point between accumulator 1 and resistance 7, and one end of a channel 18 which has its other end connected to pressure switch PS-H. Channel 5 is also connected at a point between check valve 6 and resistance 7 to pressure switch PS-L by a channel 19.

Pressure switches PS-H and PSL are alike and each has been represented as including a switch element 20, a cylinder 21 arranged above element 20 in respect to the drawing, a piston 22 fitted in cylinder 21 and connected to element 20, and a spring 23 arranged in the upper end of cylinder 21 to urge piston 22 downward. Channel 18 is connected to the cylinder 21 of pressure switch PSH at the lower end thereof and channel 19* is connected to the cylinder 21 of switch PS-L at the lower end thereof.

Contactor C1 has three normally open switches a, b and c and a magnet m for closing the switches. Current for energizing magnet C1 and solenoid 11 is supplied from two power lines L1 and L2 which are connected to opposite sides of a source of electrical energy not shown.

Pressure switch PSL has one of its terminals connected by a wire 25 to power line L1 and its other terminal connected by a wire 26 to one terminal of pressure switch PS-H and by a wire 27 to one terminal of switch C1 the other terminal of which is connected by wire 28 to power line L1. The other terminal of switch PS-H is connected by a wire 29 to one end of the winding of magnet C1 the other end of which is connected to power line L2. Switch Cl has one of its terminals connected to power line L2 and its other terminal. connected by a wire 30 to one end of the winding of solenoid 11. The other end of the winding of solenoid 11 is connected by a wire 31 to one terminal of switch Cit the other terminal of which is connected by a wire 32 .to power line L1.

The parts are shown in the position occupied when the pressure in accumulator 1 is at the desired value at which the time pump 3 is discharging through channels 5 and 15, valve body 9 and channel 16 into reservoir 4 so that pump pressure is zero. Check valve 6 is preventing accumulator 1 from discharging into channel 15. ,Accumulator pressure is extending through channels 5 and 19 to pressure switch PS-L and is holding it open. Channel 18 is open to exhaust channel 16 so that pressure switch PS-H is held closed by spring 23 but magnet C1 is not energized because the circuit therethrough is broken at switch PS-L.

When accumulator 1 discharges liquid into the circuit to which it is connected, accumulator pressure will drop. Since the pressure in switch PS-L is the same as in accumulator 1, switch PSL will be closed by its spring 23 as soon as the accumulator pressure drops below the desired value.

Closing switch PS-L establishes a circuit (L1, 25, PS-L, 26, PS-H, 29, Cl, L2) to energize magnet Cl which will close switches CI Cl and Cl. Switch C1 establishes a circuit (L1, 28, CF, 27, 26, PS-H, 29, 01*, L2) to keep magnet C1 energized when switch PS-L opens. Switches C1 and C1 establish a circuit (L1, 32, C1 31, 11, 30, Cl L2) to energize solenoid 11 which will shift valve member 8 into the position shown in Fig. 2 in which position it connects channel 118 to channel 17 and blocks the end of channel 15 so that pump 3 cannot discharge into reservoir 4. The liquid discharged by pump 3 will then flow through channel 5 to accumulator 1 to charge it. Resistance 7 resists the flow through channel 5 and thereby causes pump 3 to create in channel 19 and in switch PS-L a pressure which is higher than the pressure in accumulator 1 and which causes switch PS-L to open but contactor C1 will not open at that time because the 'c'ircuit through nagnetfl is maintained by switch C1 The pressure in accumulator 1 will extend through channels 5 and 17, valve body 9 and channel 18 to switch PS-H and, when pump 3.has delivered enough liquid to accumulator 11o raise the pressure'thereinto the'des'ired value, the pressure will open switch PS-H which will break the circuitthrough magnet 01 "and thereby cause contactorClto .open andbreak the 'circuitthrough solenoid 11. Then spring 10 will shift valve member 8 to the position shown in Fig. 1 and the parts will "be in position to start 'another'cycle 'of operations.

The pressure switches may be so adjusted that switch PS I-I will open at substantially the samepressure at which switch 'PSL c'loses 'but with such an adjustment valve member '8 wouldbe shifted almost continuously when the accumulator was discharging into the circuit unless accumulator'l had a large capacity-and was of the weight type. 'Iherefore,,s'ince small accumulators of the gas type are ordinarily desired, switch T's-H ordinarily is adjusted to. open at a pressureslightly higher than the pressure at which switch 'PSL' closes.

While the ,pump has been shown as being of the constant displacement type and the "flow icontrol .meanshas been shown as being a valve which is urgedto purnplbypassing position by a constant force and is adapted tov be shifted by .a solenoid under the control of two normally closed pressure switches which is the preferred arrangement, it is obvious that the pump-could be of .a variable displacement type and that the flowcontrol means could be a pump control which varies the displacement of the pump between zero anda predetermined maximum.

The'invention herein .set forth is susceptible of various modifications and adaptations without departing from the lscope thereof. The invention is hereby claimed as .fol

ows:

l. A system,for-.maintaining the pressure ina fluid circuit within close limits, comprising a pump connected to said circuit, flow control means connected to saidpump .and adapted to .occupyeither .a first position in which it causes said pump to deliver fluid to said circuit or a secend position in which it interrupts flow of fluid to said circuit, .means for:urging said flow control means to one .of said positions with .a substantially constant-force, .a magnetic devicefor.eifectingrnovement of said flow contrdlmeans to.the other of saidpositions, a magnetic switch for controlling said magneticadevice, and means for contrdlling the operation of, said magnetic switchincluding .twopressure switches'which open and zclosein response to variations in the pressure in said circuitand one of which-opens at apressure very close .to-the pressure at which the other one doses.

2. A system, for maintaining the pressure .in a fluid circuit within .close limits, comprising a pump connected to said circuit, .a valve .connected to said pump and adapted to .occupy either a firsf position .in which sit causes said pump to deliver fluid to'said circuit'or a second position in which it directs the .fluid -.-from said pump to exhaust, means including a magnetic :device for efiecting movement .of said valve from either to the other of said positions, a magnetic switch for controlling said magnetic device, and means for controlling the operation .of said magnetic .switch including two pressure switches which open and .close .in response .to

is connected to said valve and when said .valve .is .in

said first position said first pressure switch opens at a pressure very close to the pressure at which the second one closes and when said valve is in said second position it connects said firstpressure switch to exhaust.

3. A system, for maintaining the pressure in a fluid circuit .within close .limits, comprising a pump for supplying liquid .to said circuit, a channel connecting said pump .to said circuit andhaving a resistance arranged therein, a valve connected to said pump and adapted to occupy either a first position in which it "causes said pump to deliver fluid to said circuit or a second position in which it-directs the fluid from said pump .to :exhaust, means including a magnetic device .for effecting movement of said valve from either to the other of said positions, and means forcontrolling the operation of said magnetic device including two pressure switches one of which is connected to said circuit through said resistance and the other of which is connected 'to sald circuit through said valve, said valve having means "for connecting said other pressure switch to said circuit when said valve is in said first position and for connecting it to exhaust when said valve is in said second position. 4. A system, for maintaining the pressure in a fluid circuit within close limits, comprising a pump connected to said circuit, a valve connected to said pump and adapted to occupy either a firstposition in which it causes said pump to deliver fluid to said circuit or a second position in which it directs the fluid from said pump to exhaust, means including a magnetic device for effecting movement of said valve from either to the other of said positions, a magnetic switch for controlling said magnetic device, and means for controlling the operation .01": said magnetic switch including two pressure switches which open and close in .response to variations in the pressure in said circuit and one of which opens at .a pressure very close .to the pressure at which the other one closes.

5. A system, for :maintaining the pressure in afluid circuit within close limits, comprising va pump for supplying liquid to said circuit, a channel connecting said pump to said circuit and having a resistance arranged therein, a valve connected to said pump and adapted to occupy either a first position in which it causes said pump to deliver fluid to said circuit or a second .position in which it directs the Yfluid from said pump to exhaust, means including a magnetic device for effecting movement of said valve from either to the other of said positions, a magnetic switch for controlling said -magnetic device, and .means for controlling the operation of said magnetic switch including two pressure switches one of which is connected to said circuit through said resistance and the other of which is connected to said circuit through said valve, said 'valve;having means for connecting said other pressure switch'to said circuit when said valve is in said first position :and for connecting it to :exhaust when said valve is in said second position.

References Cited in the file of-thispatent UNITED STATES PATENTS Dunn 'Sept. 10, 1912 .Dodson Jan. 11, 1949 

